Evacuees who fled a massive wildfire that hit Fort McMurray trickle back to their homes on Wednesday, facing a massive cleanup and uncertainty over their safety as the devastated Canadian oil city begins to rebuild.

More than 90,000 residents fled the remote northern Alberta city as the fire hit four weeks ago, leaving entire neighborhoods charred in its wake. Officials expected 14,000 to 15,000 to return on Wednesday as a two-week staged re-entry begins.

The blaze, which destroyed about 10 percent of the city's homes, was a blow to a community already reeling from a two-year oil price slump. It shuttered more than a million barrels per day of crude production, though some facilities have resumed operations even as acrid smoke lingered in the air.

Speaking outside his house in downtown Fort McMurray, Mark Hebert was relieved to find his house in good shape, but his partner was worried about air quality.

"We are going to clean some stuff up here and try and cut the grass, grab a few things," the 51-year-old Hebert said.

"It's 50-50 whether we stay here tonight."

At one of the information centers in downtown Fort McMurray a brisk flow of returning residents picking up bottled water, toiletries and cleaning kits. Thanks to a specially built government website, residents know whether their houses are standing, but not how much smoke, ash and dirt seeped in during the fire.

"It's amazing. The ice is still in my fridge, it doesn't even smell like smoke," said Dawson Kohl, 47, who rents the top floor of a house downtown.

Scorched trees lined Highway 63, the only route into the city. On one overpass, a huge Canadian flag hung between two fire trucks. Billboards along the road welcomed residents home.

Authorities have told those returning to bring two weeks' worth of food, water and prescription medication. Returnees have also been told to scrub walls, and clean all clothing and bedding, upholstery of items that remained in their houses during the evacuation.

The area is under a boil water advisory and the local hospital's capabilities are limited. Some stores were open on Wednesday, and there was still smoke in the air.

Some 2,000 residents who had expected to return this week were told on Monday that they should not go back because of risks posed by debris and contaminants. Among them was Elsie Knister, 63.

"I have panic attacks, there's water damage, there are toxins in my furniture and my cupboards, and under the floor,"

Knister said. "I am scared of everything right now, and I am going to have to deal with it one day at a time."